The invention relates to crushers and preferably cone and gyratory crushers, but the arrangement can also be used in other crushers, such as impact and jaw crushers. Typically, cone and gyratory crushers are used for intermediate and fine crushing of material, such as rock. Cone crushers comprise a vertical eccentric shaft and an oblique inner hole fitted therein. A main shaft, to which a supporting cone is often fastened, is fitted in the hole. The supporting cone is surrounded by the frame of the crusher, to which has been mounted a means called an outer crushing blade and functioning as a wearing part. To the supporting cone, in turn, has been mounted a means called an inner crushing blade and used as a wearing part. The inner crushing blade and the outer crushing blade together form a crushing chamber, in which the feed material is crushed. When the eccentric shaft is rotated, the main shaft and thereby the supporting cone are entrained in an oscillating motion, wherein the gap between the inner and outer crushing blades varies at each point during the cycle. The smallest gap occurring during the cycle is called the setting of the crusher, and the difference between the maximum and the minimum of the gap is called the stroke of the crusher. By the crusher setting and the crusher stroke it is possible to influence, among other things, the grain size distribution of the crushed material and the production capacity of the crusher.
The main shaft of a typical cone crusher is bearing-mounted below the crushing cone only. In some crushers, the main shaft of the crusher is further supported at its upper end to the frame by means of an upper thrust bearing. It is this subtype of a cone crusher that is normally called a gyratory crusher.
To increase the efficiency of the crushing process and the utilization degree of the crusher, the operation of the crusher must be adjusted, as the quality and quantity of the material to be crushed vary. In typical cone crushers, the operation is adjusted by controlling the settings of the blades of the crusher. In solutions of prior art, the settings are adjusted on the basis of the power consumption (input power) and/or the crushing force. However, such an adjustment of the crusher is difficult or is not necessarily possible at all in crushers in which long strokes are used.
The gyratory crusher can normally be adjusted by means of a hydraulic system in such a way that the main shaft can be moved in the vertical direction with respect to the frame of the crusher. This makes it possible to change the setting of the crusher in such a way that the grain size of the crushed material corresponds to the grain size desired at each time, and/or to keep the setting constant as the crushing blades are worn. In cone crushers of other types, the adjustment may also be made by lifting and lowering the upper frame of the crusher and the crushing blade mounted on it, in relation to the lower frame of the crusher and the main shaft which is stationary with respect to the lower frame in the vertical direction.
It has also been found that the adjustment of the settings made on the basis of the power consumption and/or the crushing force cannot be used to influence the grain size of the crushed material in a desired way. For example, the adjustment has influenced small grain sizes more strongly and larger grain sizes less strongly. For this reason, there has been a need for the further development of control arrangements.